The present application relates to providing visual of a model produced by stereolithographic techniques such as providing gray-scale and/or color detail to the model.
The term rapid prototyping (RP) refers to a class of technologies that can automatically construct physical models from Computer-Aided Design (CAD) data. These xe2x80x9cthree dimensional printersxe2x80x9d allow designers to quickly create tangible prototypes of their designs, rather than just two-dimensional pictures. Such models have numerous uses. They make excellent visual aids for communicating ideas with co-workers or customers. In addition, prototypes can be used for design testing. For example, an aerospace engineer might mount such a model airfoil in a wind tunnel to measure lift and drag forces.
In addition to prototypes, RP techniques can also be used to make tooling (referred to as rapid tooling) and even production-quality parts (rapid manufacturing). For small production runs and complicated objects, rapid prototyping is often the best manufacturing process available. Of course, xe2x80x9crapidxe2x80x9d is a relative term. Most prototypes require from three to seventy-two hours to build, depending on the size and complexity of the object.
Because RP technologies are being increasingly used in non-prototyping applications, the techniques are often collectively referred to as xe2x80x9csolid free-form fabricationxe2x80x9d, xe2x80x9ccomputer automated manufacturingxe2x80x9d, or xe2x80x9clayered manufacturing.xe2x80x9d The latter term is particularly descriptive of the manufacturing process used in rapid prototyping commercial techniques, since a software package is used to xe2x80x9cslicexe2x80x9d the CAD model into a number of thin (e.g., approximately 0.1 mm to 0.7 mm) layers, which are then built up successively one on top of another. Thus, rapid prototyping is an xe2x80x9cadditivexe2x80x9d process, combining layers of paper, wax, or plastic to create a solid object. In contrast, most machining processes (milling, drilling, grinding, etc.) are xe2x80x9csubtractivexe2x80x9d processes that remove material from a solid block. Accordingly, the additive nature of rapid prototyping allows the creation of objects with complicated internal features that cannot be manufactured by other means.
One of the most important rapid prototyping techniques is stereolithography (STL). In fact, stereolithography started the rapid prototyping revolution in the late 1980""s. The STL technique builds three dimensional models from liquid photosensitive polymers that solidify when exposed to ultraviolet light. As illustrated in prior art FIG. 1, a model 20 is built upon a platform 22 situated just below the surface of a vat of, for example, liquid epoxy or acrylate resin. A low-power highly focused UV laser traces out the first layer, solidifying a cross section of the model while leaving the resin in a liquid state in those areas not identified as part of the xe2x80x9ccurrentxe2x80x9d model cross section. As illustrated in FIG. 1, an elevator 24 incrementally lowers the platform 22 into the liquid polymer 26. A sweeper 28 re-coats the solidified current model layer with liquid resin from the vat 30, and the laser 32 (via lenses 34 and mirror 36) traces each next layer atop the previous layer. This process is repeated until the prototype model 20 is complete. Afterwards, the solidified model 20 is removed from the vat 30 and rinsed clean of excess liquid resin. Subsequently, supports may be broken off the model and the model is then placed in an ultraviolet oven (not shown) for complete curing.
In detail, stereolithography, as well as other rapid prototyping techniques, all employ the same basic five-step process. The steps are:
Step 1 Create a CAD data model of the design;
Step 2 Convert the CAD data model to a standard stereolithographic (STL) data format;
Step 3 Manipulate the STL file so that the model to be generated is in a desired orientation and has a desire resolution by xe2x80x9cslicingxe2x80x9d the model represented by the STL file into thin cross-sectional layers;
Step 4 Construct the model one layer atop another using a STL device; and
Step 5 Clean and finish the model.
Thus, the object (i.e., model) to be built is first modeled (in Step 1) using a computer-aided design (CAD) software package. Solid modeling CAD systems tend to represent three dimensional objects more accurately than wire-frame modelers, and will therefore tend to yield better results (i.e., a more accurate model). However, regardless of the CAD packages used, to establish consistency, the STL rapid prototyping industry has adopted a standard data format for inputting data to stereolithographic model generating devices. Accordingly, in Step 2, the CAD file output in Step 1 is converted into STL format. This format represents a three dimensional surface as an assembly of planar triangles, like the facets of a cut jewel. Thus, the standardized STL output file contains the coordinates of the vertices and the direction of the outward normal of each triangle. Because STL files use planar elements, they cannot represent curved surfaces exactly.
In Step 3, a pre-processing program prepares the STL file for use by a STL device for generating the desired model. Several programs are available for this purpose, and most allow the user to adjust the size, location and orientation of the model to be built. Build orientation is important for several reasons. First, properties of rapid prototypes vary from one coordinate direction to another. For example, prototypes are usually weaker and less accurate in the z (vertical) direction than in the x-y plane. In addition, part orientation partially determines the amount of time required to build the model. Placing the shortest dimension in the z direction reduces the number of layers, thereby shortening build time. Additionally, all such pre-processing programs generate slices of the STL model into a number of layers from 0.01 millimeters (mm) to 0.7 mm thick (in the z direction), depending on the build technique and the resolution desired. The preprocessing program may also generate an auxiliary structure to support the model during the build. Supports are useful for delicate features, such as overhangs, internal cavities, and thin-walled sections.
In Step 4, the actual construction of the model is performed. Using one of several techniques RP machines build one layer at a time from polymers, paper, or powdered metal. Most machines are fairly autonomous, needing little human intervention. Subsequently, the built model may be cured so that further hardening occurs.
Finally, in Step 5, post-processing finishing is performed. This step involves removing the prototype from the machine and detaching any supports. Some photosensitive materials need to be fully cured before use. Prototypes may also require minor cleaning and surface treatment. Sanding, sealing, and/or painting the model will improve its appearance and durability.
However, in using stereolithographic techniques to build such models, the techniques for providing shading and/or color to such models have been performed by:
a. Introducing an additive into the resin such as the chemical compounds referred to in U.S. Pat. No. 5,514,519 to Neckers incorporated herein by reference. In particular, the following compounds have been added to such resins: carbon black, anthraquinone-based blue dyes, tetracyano uinodimethane, and photobleachable dyes such as: 1,3-dihydro-6xe2x80x2,8xe2x80x2-dichloro-1-hexyl-3,3-dimethyl spiro greater than 2H-indole-2,2xe2x80x2- greater than 3H!benzopyran! (SP1) and 1,3-dihydro 6xe2x80x2-nitro-8xe2x80x2-bromo-1-hexyl, 3,3-dimethyl spiro greater than 2H-indole-2,2xe2x80x2- greater than 3H!benzopyran!. Moreover, such additives may not provide visual details of the model. In particular, such prior art colorizing techniques can not easily provide multiple shades of any color. Thus, for example, visual details that could be represented by gray scale shading are typically unavailable. Accordingly, the gray scale or color representation of the bone structure in the model of a hand such as in FIG. 2 has not been easily attained theretofore, or
b. The application of a tremendous amount of laser energy to the resin (e.g., approximately 1000% of the critical energy required for resin solidification) for affecting the optical density of desired portions of the resulting STL model. In particular, the UV overcure selectively burns the solidified resin (i.e., oxidizes the resin) so that shading of the selected the portions of the model occurs immediately. Such a UV overcure technique also produces unwanted side effects including de-wetting or smoke that can accumulate in the model building chamber. Moreover, in at least one stereolithographic system having 3D Lightyear STL data model generating software by 3D Systems Inc. of Valencia, Calif., overcure values have been restricted such that the amount of laser energy required to adequately darken a model by such burning is not possible with standard build style STL data files.
Accordingly, it would be advantageous to have a system and method for selectively introducing shading and/or color variations in an STL model, wherein external and/or internal features of the model and/or indicia thereon are readily discernable. Furthermore, it would be advantageous that the system and method be cost effective and easily implemented (e.g., using existing STL technology) without requiring large amounts of energy and without producing unwanted side effects.
The drawbacks and disadvantages of the prior art are overcome by the method and system for colorizing a stereolithographically generated model.
The present invention is a system for producing stereolithographic (STL) models, wherein shading and/or color variations can be provided in or on the model. In particular, the present invention provides more visual detail of a three dimensional object (i.e., model) wherein the surface or internal structures can be more readily discerned due to the intentional shading and/or colorizing of various portions of the model differently.
Moreover, the present invention is an enhancement to the current process of creating three dimensional geometries (e.g., models) using a STL apparatus. In particular, referring to the Steps 1 through 5 above, the present invention is an enhancement of at least Steps 1 and 4, and in some embodiments such enhancements may also be directed to Step 2. More particularly, Step 1 is modified by the method and system of the present invention in that colors and/or shades (e.g., grayscale) are provided in the CAD data model in a manner that allows such colors and/or shades to be converted into a data format that is usable by an STL machine to generate the corresponding STL model with the desired coloring and/or shading. It is an aspect of the present invention to provide a plurality of color data transfer techniques to perform such data conversions wherein colors and/or shades in the CAD data model are implemented in a solid resin model. Such color data transfer techniques will be described in detail hereinbelow.
Enhancements to Step 4 may be generally described as including the following sub-steps:
Step 4.1. The slices of three dimensional data (generated in Step 3) representing layers of the model are sequentially solidified from the liquid resin 26 by a laser 32 (as illustrated in FIG. 1) outputting sufficient ultra-violet wavelength and millijoule energy onto the surface of the liquid resin to thereby harden a thin layer of the resin at the surface. In particular, such solidification is typically by means of actinic radiation;
Step 4.2. The completed model is removed from the resin vat 30 and cleaned of excess uncured resin; and
Step 4.3. The model is then exposed to additional ultraviolet light in an ultraviolet oven to further harden the model. Note that this step is required not only to further harden the model, but also because such resins in their non-solid state are typically toxic to humans and cannot be handled until completely hardened.
The improvement of the present invention adds shading and/or color to the outside and/or inside of a STL generated model by modifying Step 4.1 (or, adding a subsequent step) denoted Sub-step A below and adding a subsequent additional Sub-step B prior to Step 4.3, and more particularly between Steps 4.2 and 4.3. In particular, Sub-steps A and B are as follows:
Sub-step A. In addition to the irradiation of the resin 26 as described in Step 4.1 above for forming a layer of the model, additional laser radiation is provided to portions of the layer that is to be shaded and/or colored. The amount of additional energy (beyond what is necessary for solidifying the model) that is directed to the portions of the layer intended to be shaded and/or colorized is dependent upon the shade or color desired as well as a number of other factors such as the type of resin as well as other factors described herein below. However, the amount of additional energy beyond what is necessary for solidifying the model is in the range of 0.01% to 500%, and more particularly in the range of 10% to 100%. Further, the additional exposure to the laser radiation may not produce any visible shading in the model without subsequently performing Sub-step B following; and
Sub-step B. The model is placed in an oven and heated to 70 to 90 degrees Celsius (xc2x0 C.) from 30 minutes to 4 hours depending on various characteristics of the model (e.g., the type of resin used, the size of the model, and amount of laser energy overexposure in Sub-step A). It is during the Sub-step B that the portions of the model that received additional amounts of laser energy (i.e., overexposure or overcuring) in Sub-step A become shaded and/or colorized.
Accordingly, the present invention may be cost effectively implemented with readily available and/or currently used components in the stereolithography industry. Moreover, the ability to produce such shading and/or colorizing in STL models according to the present invention makes available new and novel model features including the ability to brand such models, provide indicia thereon, texture a model, simulate model finishing such as the appearance of paint, reproduce a photographic image applied to the inside, outside or both of such a model.